Power supply devices (electric power supply circuits) for converting alternating current power to direct current power using a rectifier circuit have been conventionally known. A power supply device of this type includes a plurality of capacitors and reactors within the circuit, and therefore, harmonics tend to be generated, which results in reduction in power supply efficiency. To prevent such the reduction in power supply efficiency, a power supply device in which harmonics are reduced by so-called PAM (pulse amplitude modulation) control is known as disclosed in Patent Document 1.
Specifically, the power supply device disclosed in Patent Document 1 includes a rectifier circuit, which is an arrangement of diodes in a bridge configuration, and a smoothing circuit having a plurality of capacitors. More specifically, the smoothing circuit is composed of two capacitors connected in series to each other, and a single smoothing capacitor connected in parallel to the two capacitors, and is configured to perform double voltage rectification between the smoothing circuit and the rectifier circuit. Further, the power supply apparatus includes a switching element, provided between an output terminal of the bridge rectifier circuit and the power supply, for short-circuiting output power of the rectifier circuit when turned on.
In the power supply device, the switching element is switched at predetermined timing according to a zero-cross point of an input voltage so that, in the rectifier circuit, a waveform of the input current approximates to a waveform (i.e., a sine wave) of an input voltage. Specifically, the power supply device is configured such that the on duty of the output waveform by the PAM control is controlled by this switching operation, and thereby, the waveform of the input current approximates to the sine wave. By this PAM control, harmonic currents generated in the power supply device are reduced.